What does what does the h stand for in h-tree? Like the b in btree is
binary Tree
Stephen Samuel wrote:
The OS will have to search the directory to see if the file already
exists before creating it.
Well, if you hash it such that it splits up something like:
jobid(upper part)/jobid(lower- part)[/-]timestamp-process,
you'll find that your access times will be must faster (especially if
you don't use H-Trees). This also applies if you're just creating a
file, because you'll have to search the entire directory to see if
that filename exists
With regular directories, searching through them to see if a file
already exist increases linearly with the number of entries. If you
hash on 3 levels with 8-bits per level, you'll have to open 2 or 3
extra inodes, but you'll cut your directory search times down by a
factor of 20000-1. You'll also skip having to deal with any sort of
directory-size limit. (=2^24/256/3)
I did something similar on a Solaris box which had 200000 emails in
the /var/spool/mqueue directory. That many messages was slowing the
system to a crawl. I hashed it into 100 directories with 2000
entries each, it sped things up *enormously.*
On Tue, Mar 18, 2008 at 3:56 PM, Andreas Dilger <adilger@xxxxxxx
<mailto:adilger@xxxxxxx>> wrote:
On Mar 17, 2008 09:32 -0400, Theodore Ts'o wrote:
> On Mon, Mar 17, 2008 at 03:40:36PM +0800, liuyue wrote:
> > Theodore Tso,
> >
> > In 64bit system, directory size can not be bigger than 2GB?
>
> No, because the high 32-bits for i_size are overloaded to store the
> directory creation acl.
I think we should change the code (kernel and e2fsprogs) to allow
i_size_high for directories also.
> In practice, you really don't want to have a directory that huge
> anyway. Iterating through it all with readdir() gets horribly slow,
> and applications that try do anything with really huge directories
> would be well advised to use a database, because they will get
*much*
> better performance that way....
Actually, for many HPC applications they never do readdir at all.
The job creates 1 file/process and always uses a predefined filename
like {job}-{timestamp}-{process} that it will directly look up.
Cheers, Andreas
--
Stephen Samuel http://www.bcgreen.com
778-861-7641
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